PRACTICAL ORGANIC CHEMISTRY
to litmus, but gives no stable salts. It is used in the prepara-
tion of malachite green (benzaldehyde green) by heating-
together dimethylaniline, benzaldehyde, and solid zinc chloride.
The product (leuco-malachite green) is then oxidised with lead
peroxide and hydrochloric acid (see p. 216),
1^0 II JC6H4N(CH8)2 -> HO~CrJI4N(CH,),
H JC8II4N(CH3)2 CflII4N(CH3)2
. -> HOC£-C6H4N(CHS)2
Base of malachite green.
The latter, in presence of the hydrochloric acid, is converted
into the hydrochloride,
HC1 = C^QH4N(CH,).2
Dimethylaniline is also used for the preparation of tetra-
methyldiaminobenzophenone(Michler's compound), which forms
the basis of many colouring matters, and is obtained by acting
upon dimethylaniline with phosgene (see p. 314),
COC12 + 2C6H5N(CH,)o = OC<
Nitrosodiraethylaniline. — It is a peculiarity of the
tertiary aromatic amines, which distinguish them from the
corresponding aliphatic compounds, that they are capable of
reacting with nitrous acid. Here the nitroso-group replaces
hydrogen in the para-position to the dimethylami no-group.
The substances, thus formed, are bases, and form salts with
acids, which dissolve in water with a yellow colour. The solu-
bility of the hydrochloride of the nitroso-bases in water
distinguish them from the nitrosamines of the secondary bases?
which are insoluble. . *